1. Field of the Invention
The present invention relates to a method of stacking and transferring plates for a lead storage battery, and an apparatus for use in the method.
2. Description of the Related Art
Plates for lead storage batteries are generally produced by the pasting method. In a well-known type of pasting method, a paste-like active material is applied onto a cast grid, the surface of the grid is simply flash-dried, and a plurality of such grids are stacked and dried by aging in an aging room. Recently, there has been much progress in enhancing the productivity of such pasted plates. The productivity of the pasted plates has been greatly improved with development of various methods, for example: the expanding method which forms a continuously reticulated frame by expanding a continuous sheet of a lead alloy, applies paste continuously to the frame, cuts the frame into plates and flash-dries the plates; and the continuous casting method which applies paste to a continuously cast grid. On the other hand, handling of plates produced successively at a high rate leaves much room for improvement. Actually, the plates individually separated after being pasted and flash-dried are manually gathered at the end of the conveyor and arranged on a pallet. Such a manual operation is inefficient, and during the manual operation, many plates are damaged or degraded by mishandling, e.g., dropping plates, and, further, workers may be injured in accidents. Thus, the manually operated process spoils the effect of the improvement made in the previous process. The mechanization of this process has been slow because the plates in this process are difficult to handle by a machine. Plates flash-dried are still soft before being dried by aging and, therefore, liable to deformation. A plate formed by the expanding method is particularly difficult to handle because the cut end portions of the plate are fragile because of its structure.
To mechanize the process of stacking and transferring such plates, various methods have been developed, for example: a method in which a plate is picked up from a belt conveyor by a belt with a sucker rotating above the belt conveyor, and released from the sucker in such a predetermined position that the released plate falls on another plate; a method disclosed in, e.g., U.S. Pat. No. 5,006,040, which uses a pair of ejection rollers to eject plates down to a belt conveyor in order to stack plates; and a method for stacking printed sheets disclosed in U.S. Pat. No. 4,934,687 in which a stacker table for receiving printed sheets is thrust out from under a pair of flying rollers. The last-mentioned method is applicable to plates. However, these methods have problems. The first-mentioned method fails to achieve constant operation due to, for example, mis-suction and mis-release from the sucker device. The second and third methods need to adjust the speed of the flying rollers or thrust the stacker table out at a high speed in order to continuously stack plates, because of the operation in which after a plate is dropped, the conveyor or the stacker table is operated. Therefore, as the transport speed of the plates is increased, the drop positions of the plates vary more significantly, resulting in more damaged plates, more accidents causing the apparatus to stop, and less precisely-registered stacking of plates, which makes it more likely that plates will fall off during the transportation of the plates for the next process. Further, many stacks of plates are collectively handled, mainly by hand, to transfer them onto a large flat board. Thus, it is necessary to develop a method and apparatus for both stacking and transferring of plates which achieves constant and continuous operation and precise register of a stack of plates, thus facilitating high-speed mass production of lead storage batteries.